A general method of transformation of living ring-opening metathesis polymerization (ROMP) into controlled/"living" atom transfer radical polymerization (ATRP) is reported for the preparation of block copolymers. For example, the macroinitiators PNB-C6H4-CH2Br (Mn = 30 520, M-w/M-n = 1.09) or PDCPD-C6H4-CH2Br (M-n = 12 100, M-w/M-n = 1.24) were prepared by ROMP of norbornene (NB) or dicyclopentadiene (DCPD) and subsequent Wittig-like reactions with p-(bromomethyl)benzaldehyde. These compounds were used as efficient macroinitiators for homogeneous controlled/"living" ATRP to prepare block copolymers with styrene (St), PNB-b-PSt (M-n = 110 400, M-w/M-n = 1.06) and PDCPD-b-PSt (M-n = 20 100, M-w/M-n = 1.37), and methyl acrylate (MA), PNB-b-PMA (M-n = 85 100, M-w/M-n = 1.07) and PDCPD-b-PMA (M-n = 25 300, M-w/M-n = 1.47).